Investigation into three dimensional ultrasound for generating vascular reconstructions suitable for diagnostic technique development

Abstract:

A three dimensional ultrasound (3DUS) system was developed with the aim of generating three dimensional (3D) vascular reconstructions. The system was required to be compatible with both a linear and a curvilinear transducer. A number of vascular phantoms were designed to recreate both shallow and deep vessels. A wall-less phantom with an agar based tissue mimicking material (TMM) and a cavity was found suitable for basic, shallow geometries. An idealised aneurysm with a silicone vessel mimicking material (VMM) represented a deeper, more complex geometry.
Image processing to improve the boundary definition was found to have an insignificant effect on the images and may be unnecessary in this application. A NDI (Northern Digital Inc., Ontario, Canada) Polaris optical tracking system and the software Stradwin were combined to form ultrasound data that was tracked through three-dimensional space. The straight tube, wall-less phantom was used to test the method with a L14-5 transducer. Three reconstructions were made and the average percentage error in radius was less than 4.5%. As it is predominantly a manual method, a user variability study, using the ideal aneurysm phantom was conducted with three operators. This comprised of the operators each taking three scans which were processed by a single individual. Four profile lines were created on each reconstruction in four anatomical positions and the asymmetry of each line, in relation to a straight line, was calculated. The highest error found was 5.17mm. Three scans taken by one operator were then processed by three operators. In this case, the highest error found was 3.22mm. The user variability was not significant, however, it was discovered that all scans overestimated dimensions and were aligned at an angle. This angle was consistent for the calibration. It was found that the application of trigonometric functions to the data rectified these issues. When the angular error of 11º was corrected, the average error in diameter reduced from 22.1% to 8.1%. The cases with 45º reduced the error from 15% to 13.5%. In one case the error increased from 11.6% to 15.8% as the technique over corrected the issue. The correction factor’s success is dependent on the angle. Overall the results indicate 3DUS provides successful reconstructions using a linear transducer and has potential with a curvilinear transducer in a laboratory setting.